The width of the frequency band available to a subscriber terminal depends on many technical solutions. The factors affecting the width of the frequency band include the antenna structure and the structure of the components connected to the antenna. The antenna needs to be able to receive and transmit signals as well as possible in all circumstances. The frequency and power of the signal transmitted via the antenna may vary considerably depending on the device, system and circumstances, so it is of essential importance for the operation of the device that the antenna should perform optimally in all situations.
In practice, all antennas need a properly functioning grounding arrangement to be able to work effectively as radiators. In the present context, the grounding arrangement for the antenna is also designated as “antenna ground”, which refers generally to the grounding circuitry used to establish a low-impedance connection to the earth potential or to a common reference point.
As the physical size of the devices is diminishing, the task of implementing the desired properties is becoming increasingly difficult. In addition, terminals are required to be able to work at ever-higher frequencies and use more frequencies besides wider and wider frequency bands. The more frequencies the device can utilize and the wider is the frequency band, the more information it can transfer. The antenna structure and the components connected to it can be used as a means of determining the width of the frequency band. Depending on its type, the antenna may be connected to the antenna ground by a short-circuiting conductor (short cut). The present invention relates especially to terminals of this category.
As stated above, the antenna must be reliable and efficient in widely varying situations and environments of application. In addition to information signals, the antenna may receive various spurious signals produced by the device's own electronics. Such spurious signals have an adverse effect on the duty signal, and spurious signals may appear in the conductors connected to the antenna and be passed further via the conductors to the antenna and further into the wireless transmission. Thus, the device itself may generate such spurious signals, some of which may be produced e.g. by harmonics associated with the clock signals of the device.
The object of the invention is to improve the construction of a terminal so as to more effectively prevent spurious signals from being passed to the antenna or to conductors connected to the antenna. An additional object is to implement a device construction that allows the frequency band of the antenna of the device to be easily increased.